public void Evaluate(string exp)
{
ExpressionBuilder expBuilder = new ExpressionBuilder();
// build the exp form the input string
IEvaluableExp evaluableExp = expBuilder.BuildExp(exp, m_EnvironmentVars);
// update new var
m_EnvironmentVars[expBuilder.Variable] = evaluableExp.GetEvaluateExpValue();
}
private IEvaluableExp BuildExpAfterAss(string exp, Dictionary <char, int> envVars)
{
if (string.IsNullOrEmpty(exp))
{
throw new InvalidExpressionException();
}
// special case "++/--" excluding ( '5++'+j )
if (exp.Length > 2 && !Char.IsDigit(exp[0]) && (exp.Substring(0, 3).Contains("++") || exp.Substring(0, 3).Contains("--")))
{
IEvaluableExp leftexp = BuildExpPre(exp.Substring(0, 3), envVars);
return(exp.Length == 3 ? leftexp :
new RegularExp(leftexp, GetOP(exp[3]), BuildExpAfterAss(exp.Substring(4), envVars)));
}
// +/- evalutint first order not important
if (exp.Contains('+'))
{
var pivot = exp.IndexOf('+');
(string lefExp, string rightExp) = SplitExpByPivot(exp, pivot);
return(new RegularExp(BuildExpAfterAss(lefExp, envVars), OpEnum.Add, BuildExpAfterAss(rightExp, envVars)));
}
else if (exp.Contains('-'))
{
var pivot = exp.IndexOf('-');
(string lefExp, string rightExp) = SplitExpByPivot(exp, pivot);
return(new RegularExp(BuildExpAfterAss(lefExp, envVars), OpEnum.Sub, BuildExpAfterAss(rightExp, envVars)));
}
// mul is evaluted last because it has priorty in calculation over (+, -)
else if (exp.Contains('*'))
{
var pivot = exp.IndexOf('*');
(string lefExp, string rightExp) = SplitExpByPivot(exp, pivot);
return(new RegularExp(BuildExpAfterAss(lefExp, envVars), OpEnum.Mul, BuildExpAfterAss(rightExp, envVars)));
}
// base case: exp is var('j') or num(79)
if (IsSimpleExp(exp))
{
return(new SimpleExp(int.Parse(exp)));
}
else
{
if (exp.Length > 1)
{
throw new InvalidExpressionException();
}
return(new VariableExp(exp[0], envVars));
}
}
public RegularExp(IEvaluableExp leftExp, OpEnum op, IEvaluableExp rightExp)
{
m_LeftExp = leftExp;
c_Op = op;
m_RightExp = rightExp;
}
